Picosecond needs for phonon dynamics in nanoscience / energy science

Yuelin Li,

X-ray Science Division, Argonne National Laboratory

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Thermoelectricity and energy future

90% of US power is from heat engines with efficiency at 30-40%, thus about 15 TW of heat is lost to the environment

Thermoelectric devices can potential convert part of these into electricity. At 1% level, this is equivalent to the total power of 100 1 GW nuclear power plants.

Solar thermoelectricity

However: efficiency/economics are the key

Figure of merit

ZT=S2T/k

K: heat conductivity

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Thermal electricity and nanoscience: Engineering in thermal electric systems

Nanoscience research for energy needs: Report of the national naothechnology initiative grad challenge workshop, http://www.sc.doe.gov/BES/reports/files/NREN_rpt.pdf

Link the function and structure at nanoscale Use nanostructure to manipulate energy carrier

– Allow electrons to flow, block phonons Figure of merit

ZT=S2T/k

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Phonon = Lattice vibration Lattice vibration of nanoparticles: optical methods

– Oscillation period T: D (particle size)/ v (sound velocity)• For gold nano particles, eg., D=10 nm

gives T=3 ps (v=3240 m/s )• Perner et al., ‘,’PRL 85, 792 (2000).• Vn Dijk et al., PRL 95, 267406 (2005).• Jerebtsov et al., PRB 76, 184301 (2007). • Courty, et al., Vibrational coherence of self-organized silver

nanocrystals in f.c.c. supra-crystals. Nature Mater. 4, 395–398 (2005).

Vibration of nano super lattice

– Layer structure, ps time scale• Trigo et al., ‘Probing Unfolded Acoustic Phonons with X-rays’,

PRL. 101, 025505 (2008)• Bargheet et al., ‘Coherent Atomic Motions in a Nanostructure

Studied by Femtosecond X-ray Diffraction,’ Science 306, 1771 (2004).

Bottom upAcoustic oscillation in a nanoparticles/structures

Self organized silver nanoparticle and vibration

GaAs/AlGaAs superlattice

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Bottom upapproachCoupling of phonon oscillation between particle via plasmon oscillation:

SPR/lattice vibration is dependent on the particle separation

Huang, et al., ‘The Effect of Plasmon Field on the Coherent Lattice Phonon

Oscillation in Electron-Beam Fabricated Gold Nanoparticle Pairs,’ Nano Letters 2007 7 (10), 3227-3234

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Top-down approachMaterials with promising Macroscopic-property (heat conductivity) Nano scale structures for low thermal conductivity (0.05

W m-1K-1), and ZT~2.4– Chiritescu et al., Ultralow Thermal Conductivity in Disordered, Layered WSe2

Crystals, SCIENCE 315, 351 (2007)

– Hochbaum et al., ‘Enhanced thermoelectric performance of rough silicon nanowires’, Nature 451, 163 (2008)

– Boukai et al., ‘Silicon nanowires as efficient thermoelectric materials,’ Nature 451, 168 (2008)

– A. Majumdar, Thermoelectricity in semiconductor nanostructures, Science 303,777 (2004).

– Venkatasubramanian, et al., Thin-film thermoelectric devices with high roomtemperature figures of merit, Nature 413, 597 (2001).

– Harmon et al., Quantum dot superlattice thermoelectric materials and devices, Science 297, 2229 (2002).

Challenges

– Phonon dynamics unknown

– Very challenging to model (for all nano sctructures!)

Disordered WSe2 layers

Silicon naowires

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Time resolved x-ray measurement:Bridge the macro to nano scales: phonon/propagation

Heat = Phonon = Lattice vibration

– Excite phonons: Laser pump

– See phonons and propagation: x-ray probe with XRD, GISAX, …… Requires ps resolution

– Ultrafast lasers: Yes – ps x-ray pulses: No – ps detector: Y&N (streak camera at Sector. 7)

– Theory and simulation We already have other resources:

– CNM, MSD, APS, U-Chicago, North-Western, and other With the ps x-ray source, we can

– better understand nanostructure for all purposes

– design better thermoelectric material for future sustainable energy source

– help others time resolved activities

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Taking LCLS into account

APS Short pulse/detector vs. LCLS– Pro:

• Existing infrastructure and collaboration• Stability, availability • Higher average photon flux• Better sample survivability

– Con• Low peak photon flux • Mentally less dazzling

LCLS pro and con– Pro

• Shorter pulse with high photon flux• Mentally more dashing

– Con• Availability and beam time allocation• Sample survivability• unwilling travel for users